1. Field of the Invention:
This invention relates to a magnetic recording medium. More particularly, this invention relates to a magnetic recording medium which is produced by applying a back coating to a thin-film type magnetic recording medium having a ferromagnetic film formed on a substrate as by electroplating, chemical plating, vacuum deposition, spattering or ion plating and which, therefore, is enable to acquire a lower friction coeffieicnt, exhibit a less inclination to curl inwardly on the ferromagnetic film side, and show a smaller possibility of inducing the phenomenon of dropout than the original thin-film type magnetic recording medium.
2. Description of Prior Arts:
Magnetic recording media have to date found extensive utility in various applications such as to magnetic tapes for use in audio and video devices, magnetic disks for use in computers and word processors, and magnetic cards for use in other household devices. In consequence of expansion of these applications, the volume of information to be recorded on such magnetic recording media is growing year after year. In the circumstance, the desirability of developing magnetic recording media of higher recording density is winning growing recognition.
When a magnetic recording layer is formed by using the technique of electroplating, chemical plating, vacuum deposition, spattering or ion plating, for example, the produced ferromagnetic film is allowed to acquire high recording density because it consists wholly of metal, alloy or an oxide thereof. When the ferromagnetic film is formed by any of the methods described above, however, the surface condition of the substrate strongly affects the surface condition of the ferromagnetic film. To be specific, when the thin ferromagnetic film is deposited by such a method on the surface of a given stustrate, the surface condition of this particular substrate exerts an effect to bear strongly upon the surface condition of the ferromagnetic film.
For the purpose of minimizing the spacing loss between the magnetic recording medium and the magnetic head and curbing the phenomemon of dropout, the surface of the magnetic recording medium is desired to be smooth. Consequently, the substrate is desired to have a smooth surface. When the substrate gains in surface smoothness, however, the magnetic tape produced by using this substrate, while in travel in the recorder, tends to cling to guide rollers and support pins.
In view of this drawback, we have already proposed a magnetic recording medium which is provided with a back coating capable of manifesting highly effective rigidification enough to overcome the shortcomings suffered by the conventional magnetic recording media. When this back coating is produced by preparing as a binder a mixture of thermoplastic resin represented by a vinyl chloride-vinyl acetate copolymer with polyurethane and an isocyanate compound or a mixture of the components just mentioned plus nitrocellulose, dipsersing a powdered non-magnetic substance in the aforementioned binder, and applying the resultant dispersion in the form of a layer, for example, there can be derived various effects such as (1) lowering the friction coefficient of the back side of the tape, (2) abating the inclination of the tape to curl inwardly on the ferromagnetic film side, (3) preventing the loss of cinching (the phenomenon of the wound tape to come loose on sudden stop of its rotation) and (4) precluding excessive clinging between the ferromagnetic film side and the back coating side of the tape.
Techniques such as this may well be concluded as basically contemplating a tape construction comprising a thin ferromagnetic film layer formed on one side of a substrate and a back coating on the other side of the substrate and using as the back coating what is obtained by dispersing a powdered non-magnetic substance in a binder containing a major proportion of thermosetting resin. The magnetic recording medium containing such a back coating as described above, as compared with the magnetic recording medium lacking the back coating, generates a further problem not associated with any of the aforementioned drawbacks. This problem is "jitter." By "jitter" is meant the phenomenon that a minute variation in phase results in vibrations of picture image. The jitter is believed to be ascribable to the smoothness of the travel of the tape in the recording device.